SBIR-STTR Award

Over the horizon radar (OTHR) systems survey large areas searching for targets several thousand kilometers away by using ionospherically reflected high frequency (HF) radio waves. Accurate coordinate-registration (CR) of the targets requires detailed knowledge of the electron density profile (EDP) of the ionosphere between the radar and the targets. Our proposal outlines a realistic path toward providing in near real-time the specification of the ionospheric electron density distribution including wave modulations caused by traveling ionospheric disturbances (TIDs). The International Reference Ionosphere (IRI) model is used as a background model. Digisondes are proposed for the measurement of the ionospheric characteristics for real-time assimilation into the IRI model: foF2, foF1, foE, hmF2, hmF1, hmE, B0, B1, and D1. This real-time procedure will create the IRI Real-Time Assimilative Model (IRTAM). The Digisondes also measure the Doppler frequencies and arrival angles of ionospherically reflected HF signals from which the TID wave parameters are derived in real-time. The detected TID electron density waves can then be superimposed on the IRTAM electron distribution. The Huang-Reinisch2006 raytracing algorithm will be used to calculate the ray path through IRTAM. A computer simulation of this process will be conducted under Phase-I.

Benefit:
The rapid EDP and TID specifications technique proposed can be directly integrated into the existing Digisonde GIRO network in support of OTHR operations. The GIRO network can also easily be expanded by deploying additional commercially available Digisondes.

Keywords:
HF sky-waves, Ionosphere, Real-Time Assimilation, Assimilative IRI model, Real-Time raytracing, EDP computer simulations, OTHR, Digisonde

Over-The-Horizon-Radar (OTHR) systems survey large areas searching for targets hundreds to thousands kilometers away. Accurate coordinate-registration (CR) of detected targets requires raytracing and accurate specification of the bottomside ionosphere. The proposed Real-Time EDP & TID (RETID) Specification System is based on the proven IRI electron density model and measurements by DPS4D ionosondes that provide the electron density profiles (EDPs) and the characteristic layer specifications. The DPS4Ds also collect the Doppler Frequency & Angles-of-arrival (AoA) Sounding (FAS) data associated with Traveling Ionospheric Disturbance (TID) wave structures. FAS measurements are also made on CW signals from transmitters of opportunity. The FAS measurements are analyzed in terms of the TID wave vector and amplitude. EDP and FAS data are ingested in real time in databases at the Lowell GIRO Data Center (LGDC). The layer characteristics foF2, hmF2, foF1, ... are assimilated in real-time in the IRI model to generate the IRI Real-time Assimilative Model ?IRTAM? which is updated every 15 min. The TID density modulation is superimposed on IRTAM forming the ?TID-IRTAM?. Using measured AoAs, the target location is specified by raytracing through the TID-IRTAM. Comparison of measured oblique ionograms between DPS4Ds with simulated oblique ionograms validates the RETID system performance.

Benefit:
The proposed RETID system takes advantage of existing ionospheric sensors, the DPS4Ds in the Digisonde Global Ionosphere Radio Observatory (GIRO) [Reinisch and Galkin, 2011], and the associated data infrastructure at LGDC. The existing instruments, the DPS4Ds, measure both the ionospheric profile specifications and the TID parameters. The RETID approach is cost effective and can be applied at any region in the world that has at least a few operating DPS4Ds. The RETID system supports operations like OTHR and HF Geolocation that measure the arrival angles of HF skywaves by providing accurate coordinate registration.

Keywords:
Othr, Coordinate Registration, Tid, Iri, Hf-Raytracing, Real-Time Assimilative Ionosphere Model